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ap chem unit 9 > unit 9 > Flashcards

unit 9 Flashcards

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1
Q

What does ΔH stand for?

A

change in enthalpy

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2
Q

What does it mean if ΔH is negative?

A

reaction is exothermic; less energy than the start

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3
Q

What does it mean if ΔH is positive?

A

reaction in endothermic; more energy than the start

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4
Q

Are all combustion reactions endo or exo thermic?

A

exothermic (heat is given off; think of an explosion, it is not taking in heat, it is giving it off)

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5
Q

Definition of specific heat?

A

amount of heat required to raise one gram of the substance 1 degree Celsius

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6
Q

What is the symbol for specific heat?

A

c (joules/ grams C)

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7
Q

What is the symbol for energy/ heat?

A

q

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8
Q

What does it mean if q is positive?

A

energy is absorbed endothermic

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9
Q

What is another meaning for bond strength?

A

bond energy (use the bond energy equation)

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10
Q

If a reaction was positive enthalpy (+𐤃H or endothermic) and positive entropy (+𐤃S or more disorder), what is 𐤃G?

A

at high temperatures it will be thermodynamically favorable at low temperatures it will be thermodynamically unfavorable

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11
Q

If a reaction was negative enthalpy (-𐤃H or exothermic) and negative entropy (-𐤃S or more order), what is 𐤃G?

A

at low temperatures it will be thermodynamically favorable;at high temperatures it will be thermodynamically unfavorable

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12
Q

When a solid melts into a liquid is that an increase or decrease in entropy?

A

increase (more motion possible in a liquid)

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13
Q

When a solid is formed when two solutions are added together is that an increase or decrease in entropy?

A

decrease (a solid allows less motion/disorder of particles) (the opposite of this would be a solid dissolving/dissociating in a solution)

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14
Q

What does it mean if q is negative?

A

energy is lost (exothermic)

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15
Q

What is the enthalpy of formation for any element in its natural state?

A

0 (zero)

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16
Q

What does positive ΔS mean?

A

more disorder in the system

17
Q

What does entropy mean?

A

randomness or disorder of a system

18
Q

What does ΔS stand for?

A

entropy

19
Q

What does negative ΔS mean?

A

less disorder in the system; more order

20
Q

The enthalpy (𐤃H) for any element in its natural state is…

A

ZERO (ex. O2 has an enthalpy of zero when it is a gas)

21
Q

What is the equation for bond energy?

A

sum of the energies of reactants - sum of energy for products

22
Q

The entropy of a pure solid at absolute zero is…

A

Zero (you will rarely see this because we typically work in standard conditions)

23
Q

Entropy is measured in…

A

Joules (mole-1) (Kelvin-1)

24
Q

If 𐤃G is greater than zero what does it mean about the reaction?

A

It is NOT thermodynamically favorable (you can force the reaction but the products will turn right back into the reactants)

25
Q

If 𐤃G is less than zero what does it mean about the reaction?

A

It IS thermodynamically favorable (the reaction will proceed in the forward direction)

26
Q

What does it mean if 𐤃G is zero?

A

Reaction at equilibrium.

27
Q

If a reaction was negative enthalpy (-𐤃H or exothermic) and positive entropy (+𐤃S or more disorder), what is 𐤃G?

A

NEGATIVE; the reaction will be thermodynamically favorable no matter what the tempurature

28
Q

If a reaction was positive enthalpy (+𐤃H or endothermic) and negative entropy (-𐤃S or more order), what is 𐤃G?

A

POSITIVE; the reaction with be thermodynamically unfavorable no matter what the tempurature

29
Q

When a solid or liquid becomes a gas is that an increase or decrease in entropy?

A

increase (more motion allowed in a gas than a solid or liquid)

30
Q

When a gaseous chemical reaction produces more molecules is that an increase or decrease in entropy?

A

increase (there are even more randomly moving particles)

31
Q

When the temperature of a substance decreases is that an increase or a decrease in entropy?

A

decrease (as energy decreases, the particles slow down and become more ordered) (the opposite of this is when temperature increases)

ap chem unit 9 (1 decks)

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